Organizations that choose to deploy Virtual Desktop Infrastructure (VDI) are often forced to use two separate networking technologies. First, there is the Ethernet-based LAN/WAN that allows users to connect to their virtual desktops. Second, there is the Fibre Channel SAN that allows virtual desktops running on clustered host servers to access virtual hard disk files residing in centralized storage.

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Although the combined use of Ethernet and Fibre Channel networks have long been standard in VDI deployments, the use of two separate networks is far from optimal. After all, having two separate networks means separate cabling, security policies and even management tools.

In an effort to simplify network architecture, some organizations are converging their data and storage networking for virtual desktop infrastructure through the use of Fibre Channel over Ethernet (FCoE).

The benefits of FCoE for networking for VDI

There are several benefits to deploying FCoE in a VDI environment. One such benefit is the reduction in network management overhead. FCoE allows organizations to manage their Fibre Channel networks using the same software they already use for Ethernet networks.

What's more, because FCoE encapsulates Fibre Channel frames within Ethernet packets, organizations that choose to adopt FCoE won’t have to do away with their existing investment in Fibre Channel. FCoE will be compatible with most of the Fibre Channel infrastructure that is already in place. One notable exception is that it takes an FCoE switch to act as a bridge between FCoE and existing Fibre Channel hardware.

One of the biggest benefits to using FCoE is that in Ethernet environments, Quality of Service (QoS) is often used to prioritize network traffic and allow bandwidth to be reserved for specific purposes. By passing Fibre Channel traffic over Ethernet, it becomes possible to prioritize VDI traffic from storage through QoS.

Storage vendors often claim that FCoE saves money because it requires fewer networking adapters and switch ports, as well as less network cabling once you converge your two networks. However, these claims can be somewhat misleading.

It is worth noting that the converged network adapters required for FCoE are priced similarly to Fibre Channel adapters. Technically, you could replace a pair of Fibre Channel Host Bus Adapters (HBAs) and a pair of Ethernet adapters with two converged network adapters (CNAs). However, doing so would limit a server’s total available network bandwidth.

More importantly, replacing a pair of NICs and a pair of Fibre Channel HBAs with a pair of CNAs can impact redundancy. Worse yet, if a CNA were to fail, both the Ethernet stack and the Fibre Channel stack would be affected.

In the case of VDI servers, it is advantageous to install more than two CNAs. Even so, it is also important to remember that CNAs typically cost as much as Fibre Channel HBAs.There are some VDI server functions that simply will not benefit from a CNA.

For example, clustered VDI servers typically make use of an isolated network segment for heartbeat traffic. The heartbeat is used to monitor the health of the various nodes in the cluster. This isolated segment would in no way benefit from a CNA. It is better to use a standard Ethernet adapter.

The same concept also applies to server management traffic. Some VDI platforms recommend that you create a dedicated backbone segment for server management traffic. Again, there is no benefit to using CNAs on these types of segments. Standard Ethernet is completely adequate.

Based on this type of configuration, it would be overkill to fill each of the server’s expansion slots with CNAs. You would be better off installing a multi-port Ethernet adapter in one expansion slot, and then using the remaining slots for CNAs.

Cabling considerations for converged storage networking for VDI

Even though the term FCoE makes it seem as though you can use standard twisted pair cable for Fibre Channel, there are only two types of cables that can be used with FCoE. One option is to use Twinax copper cables with SFP+ transceivers (sometimes referred to as SFP+ Copper). These cables are relatively inexpensive (comparatively speaking), but they are designed for short range use. Typically SFP+ copper can be used to a maximum distance of 10 meters, although there are technologies that claim to support longer runs. The other option is to use optical cables, which are more expensive, but support longer runs.

ABOUT THE AUTHOR:Brien M. Posey, MCSE, is a Microsoft Most Valuable Professional for his work with Windows 2000 Server and IIS. He has served as CIO for a nationwide chain of hospitals and was once in charge of IT security for Fort Knox. As a freelance technical writer, he has written for Microsoft, TechTarget, CNET, ZDNet, MSD2D, Relevant Technologies and other technology companies.

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